The present disclosure relates to a lifting tool for opposing twisting of generally submerged ropes. More precisely, the present disclosure relates to a lifting tool for opposing twisting of generally submerged ropes where the lifting tool comprises a body having an operable lock that is adapted to catch a rope connector, and a structure that is designed to be connected to a hoist or a crane.
During hoisting operations at sea where heavy items having weights on the order of several hundred tons are to be disposed on the seabed, the availability of steel ropes having sufficient combined strength and length has become a limiting factor for the size of items that can be handled. The seabed may be located several kilometers below sea level, and the weight of the steel rope therefore becomes significant.
It may therefore be necessary to use fiber ropes that have a density close to that of water, to allow the largest items to be submerged into deep waters.
The use of fiber ropes for operations of this type requires consideration of conditions not normally problematic when using steel ropes. For example, the effective life of a fiber rope, which includes a significant proportion of carbon fiber, depends directly on the number of load-related flexures that the fiber rope is exposed to.
Oftentimes, hoisting operations of this type are heave-compensated, and the lifting rope will therefore be continuously reeled in and out from a winch due to the heave motion of the lifting vessel. Even if the item being lifted is stationary relative to the seabed, the lifting rope will still be reeled in and out, whereby the effective life of a fiber rope is reduced relatively quickly.
Norwegian Patent Application 20090729 discloses a method for paying out a relatively long fiber rope, which carries a load, by means of a shorter steel rope. The method, which includes the use of parallel ropes, is explained in detail in that application document.
A problem when utilizing parallel ropes is the tendency of the rope to twist and to get entangled in each other. As the ropes have to be moved independently of each other in the sea, an entanglement may in a worst case lead to cutting of the ropes and loss of a valuable item.